Found in Popular Electronics from the 90s, this circuit is based on a PLL567 and employs high-end or ultrasonic speakers depending on the frequency of oscillations.
This basic oscillator with tunnel diode generates a 100 kHz signal with 1 uW output power. The...
This amplifier for medium or high impedance magnetic headsets (above 200 ohms) was found in an...
This circuit provides precise signals of three frequencies, using CMOS technology. The integrated...